Many schemes and apparatus have been devised to produce multilayer thin films. These films are used in semiconductor fabrication, optical waveguides, and highly reflective mirrors such as those used in ring laser gyroscopes. Sputter deposition usually takes place in a vacuum chamber where a target material is impacted by ion beams to sputter material off the target by collision mechanics. This sputtered material would then be deposited on a substrate to produce the device.
Several problems have been associated with prior art systems. It has been difficult to generate a beam of ions which is free of contaminants and of a high enough energy to be effective. It has also been difficult to impart enough energy to the sputtered material to ensure a uniform deposited film of a known thickness, density and surface smoothness. The major problems, therefore, have been with the source of the ions to perform the sputtering. Ionizing sources and methods have, therefore, been the subject of significant work.
The simplest of these ionizing methods was to use a filament, or thermionic emitter, to generate electrons within the ionization chamber. The electrons created by the filament collided with the gas molecules, knocking off electrons from the gas molecules to cause the molecules to become positively charged. This method, although operable, had several disadvantages. The filaments tended to have a short life. Because the filaments were thermionic emitters and were at a negative electrical potential relative to the ionized gas, material was sputtered or evaporated off of the filament which caused contamination to be introduced into the ion beam.
An improvement upon the filament type of ion generation was the introduction of a hollow cathode. This eliminated the need of a filament and greatly increased the operational life. Potentials for contamination of the ion beam due to materials present in the hollow cathode were still present.
Further advances of ion beam generating devices included using a high-frequency generator coupled to either plates or coils within the chamber to ionize the gas molecules through excitation by the high-frequency energy. These materials, especially coils within the plasma field, also created contamination in the ion beam. An advancement, placing a coil outside the gas chamber helped to eliminate this contamination. However, external magnetic fields were usually required to contain the plasma within the chamber, enhancing ionization efficiency and to prevent arcing from the plasma to various components within the chamber. The arcing could cause a rapid degradation of the plasma and ultimate destruction of the components within the chamber. Most of the attempts to use high-frequency plasma generation also required that the generator coil be cooled by internal water means. This introduced the problem of having each end of the coil at the same potential, preferably ground potential, to prevent the high-frequency energy from being bled off to ground. Elaborate matching networks, or tight control of the length of the waveguide or coil, were required in order to accomplish these goals.
A need, therefore, exists for being able to generate a beam of positively charged gas molecules without contaminating the beam by the plasma touching contaminating fixturing within the chamber and without the need of water cooled coils or external magnetic fields.
A need also exists to translate substrates within the deposition chamber to insure uniform deposition.
A further need exists to be able to translate targets within the deposition chamber to produce multilayer films.